Breath analysis device with regulated flow during exhalation

ABSTRACT

A pump-less breath analysis device regulates the flow of breath past an analyte sensor, which may be a semiconductor sensor, by dynamically adjusting the state or position of a valve as the user exhales into the device. The valve controls the flow of incoming breath between two flow paths: a venting path through which breath exits the device without passing by the sensor, and a sensing path that includes the sensor. In some embodiments, the valve is controlled by a processor that monitors pressure produced by the user&#39;s exhalation force. Based on these real-time pressure measurements, the processor adjusts the valve to maintain the pressure, and thus the flow rate, in the sensing path within a desired range. The processor may also use the pressure measurements to determine whether the characteristics of the user&#39;s exhalation are sufficient to generate a valid measurement.

PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No.16/837,780, filed Apr. 1, 2020, which claims the benefit of U.S.Provisional Appl. No. 62/847,106, filed May 13, 2019. The disclosures ofthe aforesaid applications are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to breath analysis devices for measuringketones or other analytes in breath.

Description of the Related Art

Various types of breath analysis devices exist for allowing individualsto measure their breath ketone levels, such as acetone levels. Thesedevices are sometimes provided to participants in health programs, suchas Keto diet programs, to enable the participants to monitor fatmetabolism.

Many commercially-available breath analysis devices use a nanoparticlesensor, or another type of semiconductor sensor, to measure ketone orother analyte levels. Although these devices are typically small andconvenient to use, they typically do not generate accurate ketonemeasurements. As a result, they typically are not useful for non-Ketodiet applications in which it is desirable to measure ketone levelsfalling below about 9 parts per million (PPM).

SUMMARY

One known method for improving measurement accuracy in these types ofdevices is to include within the device a pump that controls the flowrate of the breath sample past the nanoparticle sensor. The use of apump, however, adds to the cost and complexity of the device, andtypically requires the device to include or attach to a breath capturechamber that captures the breath sample before it is pumped. Further,the task of capturing the breath sample before it is analyzed introducesdelay into the ketone measurement process.

The present disclosure addresses these deficiencies by providing apump-less breath analysis device that regulates the flow of breath pastan analyte sensor, which may be a semiconductor sensor, by dynamicallyadjusting the state or position of a valve as the user exhales into thedevice. The valve controls the flow of incoming breath between two flowpaths: a venting path through which breath exits the device withoutpassing by the sensor, and a sensing path that includes the sensor. Insome embodiments, the valve is controlled by a processor that monitorspressure produced by the user's exhalation force. Based on thesereal-time pressure measurements, the processor adjusts the valve tomaintain the pressure, and thus the flow rate, in the sensing pathwithin a desired range. The processor may also use the pressuremeasurements to determine whether the characteristics of the user'sexhalation are sufficient to generate a valid measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a breath analysis device according to one embodiment.

FIG. 2 illustrates a process implemented by the processor of the breathanalysis device during a breath test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a handheld, pump-less, breath analysis device 28according to one embodiment. The device includes a housing 30 thathouses a nanoparticle-based ketone sensor 32, a pressure sensor 34, aprocessor-controlled valve 36, internal tubes or conduits for the flowof breath along the flow paths shown by the arrows, and a processor andassociated electronics (not shown). The breath analysis device 28 alsoincludes a breath input port 40 into which a user can blow or exhale abreath sample. The nanoparticle sensor 32 is preferably designed tomeasure breath acetone levels. The device is preferably sized to fit inthe hand of the user during use.

Breath exhaled into the breath input port 40 exits the device along flowpath 1 (FP1) and flow path 2 (FP2), with the fraction exiting along FP1versus FP2 depending upon the degree to which the valve 36 is open.Because the breath flows along these paths FP1 and FL2 as the directresult of the exhalation force created by the user, no pump or otherpressure-creating device is needed. The processor-controlled valve 36preferably includes or is coupled to a stepper motor capable ofadjusting the valve between a plurality of partially-open positions. Thenumber of such positions is preferably at least 8, and can besignificantly higher. An optional one-way valve 42 at the effluent endof flow path 2 prevents air from flowing back into the device. As shownin FIG. 1 , a second pressure sensor 44 may optionally be positionedalong flow path 2. Breath that flows along flow path 2 passes by thenanoparticle sensor 32 and is used to generate a ketone measurement.Flow path 2 is thus a “sensing path,” and flow path 1 a “venting path.”As explained below, the venting path, FP1, may be omitted in someembodiments.

The device 28 may also include a wireless transceiver, such as aBluetooth or Bluetooth Low Energy (BLE) transceiver, that enables thedevice 28 to communicate wirelessly with a mobile application running ona phone, tablet, or other communication device of the user. In addition,the device 28 may include an LED, a sound generator, a haptic signalgenerator, a display, and/or another type of signal generator forconveying device status information to the user (as explained below).The device 28 may also include any of the structures and featuresdisclosed in U.S. patent application Ser. No. 15/156,188, filed May 16,2016, the disclosure of which is hereby incorporated by reference.

To obtain an accurate ketone measurement, the rate at which breath flowsalong the sensing path FP2 (and thus past or along the nanoparticlesensor 32) should be tightly regulated. In the illustrated embodiment,the task of regulating this flow rate is controlled by theprocessor-controlled valve 36 based on real-time pressure measurementsgenerated by one or both of the pressure sensors 34, 44. Morespecifically, based on the real-time pressure measurements, theprocessor controls the state of the valve 36 (and specifically thedegree to which it is open) during exhalation to maintain the pressurein the region of the nanoparticle sensor 32 within a selected range,such as 14.45-15.10 pounds per square inch (psi), 14.45-14.70 psi,14.45-14.80 psi, 14.45-14.90 psi, 14.60-14.80 psi, 14.65-14.90 psi,14.65-15.0 psi, 14.75-15.10 psi 14.45-14.60 psi, 14.45-14.70 psi,14.45-14.80 psi, 14.45-14.90 psi, 14.60-14.80 psi, 14.65-14.90 psi,14.65-15.0 psi, or 14.75-15.10 psi.

By maintaining the pressure within this range, the valve also maintainsthe flow rate past the nanoparticle sensor within a desired range, suchas 3.50-5.50 liters per minute (LPM), 5-8 LPM, 5-10 LPM, 10-12 LPM,10.25-12.50 LPM, or 12-25 LPM.

Thus, for example, if the user blows harder than average in oneembodiment, the processor partially closes the valve relative to itsmiddle or average state (e.g., from 50% open state to 35% open) tocompensate for the higher-than-average pressure in the chamber upstreamfrom the valve 36. If the user exhales with less than an average force,the processor partially opens the valve relative to its average state(e.g., from 50% open to 65% open) to compensate for the lower-thanaverage pressure upstream from the valve 36. And if the user exhaleswith a force that varies over time, the processor varies the valveposition substantially in real time to compensate for the pressurevariations upstream from the valve 36.

During exhalation, the pressure downstream from the valve 36 willordinarily be lower than the pressure upstream from the valve bypredictable amount that depends on the state of the valve; thisrelationship between upstream pressure, downstream pressure and valvestate can be recorded in a look-up table stored in a memory of thedevice 28, and can be used to dynamically control the valve.

Thus, in some embodiments, the processor may control the valve 36 basedon a look-up table (or alternatively an equation) that maps pressurereadings sensed by the upstream pressure sensor 34 to valve positions.The downstream pressure sensor 44, if provided, may alternatively beused as the source of pressure readings used to control the valve 36, ormay be used as a secondary source of real-time pressure data forcontrolling the valve. In some embodiments in which a downstreampressure sensor 44 is provided, real-time pressure measured by thissensor may be used to implement a feedback loop that seeks to minimizethe difference between the actual downstream pressure and the targetdownstream pressure. In some embodiments in which both an upstream and adownstream pressure sensor are provided, the processor controls thestate of the valve 36, and thus regulates flow, based on thedifferential pressure between the upstream pressure sensor 34 and thedownstream pressure sensor 44. For example, a look-up table or equationthat maps differential pressure to valve position may be used, or afeedback look may be used that seeks to maintain the differentialpressure approximately constant during exhalation.

FIG. 2 illustrates one example of a process that may be implemented bythe breath analysis device 28 when a user exhales a breath sample. Thisprocess may be implemented by the processor under the control of programcode (e.g., firmware instructions) stored in a memory of the device. Theprocessor may, when the device 28 is turned on, perform a warm-up cycle(not shown) to prepare the nanoparticle sensor 32 for use. Uponcompletion of the warm-up cycle, the device 28 may output a signal (suchas by illuminating an LED or outputting a sound) to inform the user thatit is ready to accept a breath sample. At this point the process entersinto a loop in which it monitors the upstream pressure to determinewhether the user is exhaling into the device. If the pressure increasesby selected threshold (e.g., over a selected time interval such as 0.5seconds, 1 second, 2 seconds, etc.), the process treats the pressureincrease as the initiation of an exhalation event (block 60).

As illustrated by block 62, the process then optionally vents an initialportion of the exhaled breath sample from the device 28 by placing ormaintaining the valve 36 in a position in which all or substantially allincoming breath is routed out along the venting path, (FP1 in FIG. 1 ).The valve 36 may be maintained in this position long enough to vent the“dead space” air in the user's trachea and lungs from the device, sothat the breath that is subsequently routed along the sensing path (FP2)consists essentially or entirely of deep alveolar breath. The ventingtime may be a fixed value in the range of about 2 to 4 seconds, or maybe a variable value that is dependent upon the pressure level sensed bythe upstream pressure sensor 34, the user's average exhalation durationas measured by the device, and/or other factors. Although such ventingof the initial breath sample portion can improve the accuracy of ketonemeasurements, it is not required.

In block 64, the process enters into a “regulated flow” state in whichthe valve 36 is dynamically controlled so as to maintain the pressuredownstream from the valve within a target range, such as one of thepressure ranges listed above, during exhalation of alveolar breath. Asexplained above, the purpose of this step is to maintain the alveolarbreath flow rate past the nanoparticle sensor 32 at a desired, andapproximately constant level (or within an acceptable range) for asufficient time period (e.g., 1 to 5 seconds) for the nanoparticlesensor to generate an accurate ketone measurement (block 66). This isaccomplished by dynamically varying the size of the valve's openingthrough which breath must flow to reach the nanoparticle sensor. Asmentioned above, the flow may be regulated based on real-time readingsfrom an upstream pressure sensor 34, from a downstream pressure sensor44, or from both an upstream and a downstream pressure sensor (e.g.,based on the real-time difference between the upstream and downstreampressure).

In decision block 68, which may be performed either during or after thetask of generating the ketone measurement, the process determineswhether the exhalation characteristics during the regulated flow phasesatisfy the criteria for generating a valid ketone measurement.Preferably, this involves determining whether the pressure downstreamfrom the valve 36 remains (or remained) within a target range for aselected time interval, such as 3 seconds, 4 seconds, or some otherduration. For example, the process may generate the ketone measurement 7seconds after exhalation begins, and may treat this measurement asinvalid if the downstream pressure did not remain in the target rangefor the 3-second time period starting at 4 seconds from initiation ofexhalation. In embodiments in which the device 28 includes a downstreampressure sensor 44, this task 68 is preferably performed based partly orwholly on the pressure monitored by that sensor 44. If no downstreampressure sensor 44 is provided, the pressure monitored by the upstreampressure sensor 34 may be used. A ketone measurement may be treated asinvalid in block 68 if, for example, the user did not blow hard enough,did not blow long enough, or did not blow with a sufficiently constantforce.

As indicated by block 70 in FIG. 2 , if the exhalation did not satisfythe criteria for generating a valid ketone measurement, the device 28outputs an error signal. For example, the device may change the color ofan LED to red, may output an error tone, and/or may transmit an errormessage to the user's mobile phone for display by a mobile application.As indicated by block 72, if the exhalation characteristics weresatisfactory, the device 28 outputs a success signal and transmits theketone measurement to the mobile device for display by the mobileapplication.

In some embodiments, the processor of the breath analysis device 28 (orpossibly the processor of a separate device) may execute a compensationalgorithm that adjusts the ketone measurement to compensate for animperfect or incomplete exhalation. For example, if the user'sexhalation falls within the acceptable pressure range but is at the lowend of that range (resulting in a lower than ideal pressure and flowrate at the nanoparticle sensor 32), the compensation algorithm may bumpup, or otherwise adjust, the ketone measurement to account for thelower-than-ideal flow rate. Pressure data collected from the pressuresensor 34 may be used for this purpose. The amount of the adjustment maybe determined by the processor using, e.g., a look-up table that mapsaverage pressure values to ketone adjustment values. Such a look-uptable may be generated using test data collected from actual orsimulated exhalation tests in which gas with a known acetoneconcentration is passed through the device at various pressure levelsand flow rates.

The accuracy of the ketone measurements can further be improved byreducing the quantity of moisture in the breath sample before it comesinto contact with the nanoparticle sensor. Thus, although not shown inFIG. 1 , the breath analysis device 28 may be configured to receive adisposable moisture-absorption element containing a desiccant. Forexample, the housing 30 may be configured to receive an insertabledesiccant cartridge that, when inserted, becomes part of the sensingflow path (FP2) upstream from the nanoparticle sensor 32. The cartridgemay be a single-use cartridge, or may contain enough desiccant formultiple breath tests. As a further enhancement, a moisture sensor (notshown) may be provided along the sensing flow path and used to determinewhether the moisture content is too high (e.g., exceeds a selectedthreshold) for generating a valid ketone measurement. If the moisturelevel is too high, the device 28 may output a corresponding error signalindicating to the user that the desiccant cartridge needs to bereplaced.

The likelihood of the user completing an exhalation of sufficientduration can be increased significantly by notifying the user of howmuch longer they need to exhale. Thus, in some embodiments, during theexhalation process, the breath analysis device 28 and/or the mobileapplication outputs an indication how much longer the user needs toexhale. This indication may, for example, be a visual, audible, orhaptic signal that is output by the breath analysis device 28 when aselected amount of time, such as one second or two seconds, remainsbefore exhalation is complete. For instance, an LED that is visibleduring exhalation may be illuminated in a particular color or strobed atthis point in time. As another example, the mobile application maydisplay a numerical countdown timer, or may display a graphicalindication of the amount of time remaining. In embodiments in which theuser is required to exhale a threshold volume of breath, the breathanalysis device's processor may determine or estimate the amount of timeremaining based on the output of the pressure sensor 34 or a flowsensor. In embodiments in which the user is required to exhale for afixed amount of time, the processor may determine the amount of timeremaining based solely on a timer that is started when the user beginsto exhale.

In other embodiments of the device 28, the venting path FP1 may beeliminated, or may be included but only used to vent an initial portionof the breath sample from the device. In these embodiments, when theuser is blowing too hard, the processor, by adjusting the state of thevalve, narrows the opening through which breath must flow to reach thenanoparticle sensor, causing the user to experience more flow resistanceand reducing the rate of flow. And when the user is not blowing hardenough, the processor adjusts the valve in the opposite direction toexpand the opening and reduce the flow resistance experienced by theuser, enabling the user to exhale at a greater flow rate.

In embodiments in which the venting path is eliminated, the valve 36 mayoptionally be positioned downstream from the nanoparticle sensor 32. Inaddition, because the initial portion of the breath sample flows pastthe nanoparticle sensor in these embodiments, the processor mayeffectively ignore the output of the nanoparticle sensor during thisstage. For example, the output of the nanoparticle sensor may beignored, or the nanoparticle sensor may be disabled, for the first Nseconds of the exhalation, where N may, for example, be in the range of2 to 5 seconds, and more preferably is in the range of 3 to 4 seconds.

Another variation is to use a flow rate sensor in place of the pressuresensor(s) 34, 44. For example a flow rate sensor may be positioneddownstream from the valve 36 and used to measure the rate of flow pastthe nanoparticle sensor 32; the processor may in turn use the output ofthis flow rate sensor to adjust the valve so as to regulate the flowrate during exhalation.

Although the designs disclosed herein are particularly useful formeasuring breath ketone levels (and particularly breath acetone levels),they may also be used to measure other breath analytes. Thus, thenanoparticle-based ketone sensor 32 in the disclosed designs may bereplaced or supplemented with a nanoparticle-based or other sensorcapable of measuring one or more other analytes.

What is claimed is:
 1. A portable breath analysis device, comprising: abreath input port fluidly coupled to a flow path; an analyte sensorpositioned along the flow path, the analyte sensor capable of measuringa level of an analyte in a breath sample that passes along the flow pathunder an exhalation force created by a user; a valve positioned alongthe flow path; and a processor configured to regulate a rate of flow ofthe breath sample past the analyte sensor by adjusting a state of thevalve during exhalation of the breath sample by the user, the processorthereby configured to compensate for variations in an exhalation forcecreated by the user.
 2. The portable breath analysis device of claim 1,further comprising a pressure sensor positioned along the flow path,wherein the processor is configured to control the state of the valvebased at least partly on pressure measurements generated by the pressuresensor.
 3. The portable breath analysis device of claim 2, wherein thevalve is positioned upstream from the analyte sensor, and the pressuresensor is positioned upstream from the valve.
 4. The portable breathanalysis device of claim 3, further comprising a second pressure sensorpositioned downstream from the valve, wherein the processor isconfigured to adjust the state of the valve based additionally on anoutput of the second pressure sensor.
 5. The portable breath analysisdevice of claim 4, wherein the processor is configured to adjust thestate of the valve based at least partly on a differential pressurebetween the upstream pressure sensor and the downstream pressure sensor.6. The portable breath analysis device of claim 1, further comprising aflow rate sensor positioned along the flow path, wherein the processoris configured to control the state of the valve based at least partly onflow rate measurements generated by the flow rate sensor.
 7. Theportable breath analysis device of claim 1, wherein the valve is coupledto a second flow path through which a portion of the breath sample isvented from the portable breath analysis device without passing by theanalyte sensor.
 8. The portable breath analysis device of claim 1,further comprising a stepper motor mechanically coupled to the valve,where in the processor adjusts the state of the valve by controlling thestepper motor.
 9. The portable breath analysis device of claim 1,wherein the analyte sensor is a ketone sensor.
 10. The portable breathanalysis device of claim 1, wherein the analyte sensor is asemiconductor sensor.
 11. A process performed by a breath analysisdevice, the breath analysis device comprising a breath input portfluidly coupled to a flow path and comprising an analyte sensorpositioned along the flow path, the process comprising, under control ofa processor of the breath analysis device: as a user exhales a breathsample into the breath input port, regulating a rate of flow of thebreath sample along the flow path and past the analyte sensor byadjusting a state of a valve; and measuring a concentration of ananalyte in the breath sample with the analyte sensor.
 12. The process ofclaim 11, wherein the state of the valve is adjusted based at leastpartly on pressure measurements generated by a pressure sensor of thebreath analysis device.
 13. The process of claim 11, wherein the stateof the valve is adjusted based at least partly on a differentialpressure between an upstream pressure sensor positioned upstream fromthe valve and a downstream pressure sensor positioned downstream fromthe valve.
 14. The process of claim 11, wherein the state of the valveis adjusted based at least partly on an output of a flow sensor thatmeasures a flow rate along the flow path.
 15. The process of claim 11,wherein the state of the valve is adjusted by controlling a steppermotor that is mechanically coupled to the valve.
 16. The process ofclaim 11, wherein the analyte sensor is a ketone sensor.
 17. The processof claim 11, wherein the analyte sensor is a semiconductor sensor.